Shop OBEX P1 Docs P2 Docs Learn Events
Efficient 120v AC -> 3v dc power supply — Parallax Forums

Efficient 120v AC -> 3v dc power supply

RegorRegor Posts: 19
edited 2008-03-17 21:53 in General Discussion
I want to do some experimenting with Zigbee sensors throughout my house. I'm looking for advice on the best compromise between power consumption and convenience. I don't want to use just battery packs since I'd have to be going around replacing them and having a bunch of AC/DC converters continually plugged into the wall sounds like a power waste.

So a couple of questions:
1) Is·the·Power Loss in an·AC/DC adapter significant or is the loss so minimal that I shouldn't even worry about it?

2) Assuming the answer to 1 is that it is wasteful are there any battery chargers that completely shut themselves off from the AC Supply?·The charger would then have to monitor the batter and then automatically turn back on the AC supply for charging. There would be a tradeoff here between the monitoring circuit vs. the lost AC/DC power.

3) Since I'll have a propeller going off the supply·the propeller itself·could be used for monitoring and controlling the relay to turn on the AC supply. Has anyone done something like this and if so did it really save any power?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-03-17 21:53
    There's always some loss in an AC/DC adapter. The amount depends on the specifics of the adapter. Most 6-10W switching regulators quote an efficiency around 70% at full load, probably a lot less at very light loads, but they don't specify that. If you use a charger instead, you'll have greater losses in charging the battery although the charger could be off most of the time. To do that, you would use an SSR to turn the power supply on and off. I've not seen any ready made.

    The Propeller could certainly monitor its own supply voltage and turn on a charger when needed.

    With a low power AC/DC switching regulator, you're probably not going to save that much. I don't know for sure and the manufacturer's datasheet for the ones I looked at don't give an idle current. At full load, the current drawn is about 60mA. 30% of that is about 20mA. I'm sure a lot of that is resistive loss so with a light output load, the input drawn is probably well under 10mA. Maybe someone else has a real figure for this.
Sign In or Register to comment.